Apparatus and process for coating a flexible web



Aug. 8, 1961 c. F. LE CLAIRE 2,995,4

APPARATUS AND PROCESS FOR COATING A FLEXIBLE WEB Filed Aug. 21, 1957CHILL HID UP AREA v21 INVENTOR CHARL ES FRANCIS (.eCLA/RE COATINGSTATION BY M ' ATTORNEY material onto supporting webs.

2,995,469 7 APPARATUS AND PROCESS FOR COATING A FLEXIBLE WEB CharlesFrancis Le Claire, Little Silver, NJ., assignor to E. l. du Pont deNemours and Company, Wilmington, 'DeL, a corporation of Delaware FiledAug. 21, I957, Ser. No. 679,342

' 9'Claims. (Cl. 117-102) This invention relates toweb coating apparatusand more particularly to apparatus for applying to continuous websviscous aqueous solutions as layers of high uniform quality in themanufacture of photographic films. and

7 papers. Still more particularly, it relates tosuch apparacombinationof such devices effects a surprising improvement in the smoothness anduniformity of quality of the appliedcoating. The apparatus according tothis invention also unexpectedly permits an increase in coating speed byas much as 300% or more without sacrifice of quality. An object of thisinvention is to provide an improved coating apparatus for producing asmooth uniform coating of material onto a travelling web. Another objectis to provide such apparatus that permits the coating'of viscous liquidmaterials ontocontinuous webs over a wide range of speeds; Yet anotherobject is to provide such apparatus that is easily adjustable andaccessible for cleaning and maintenance. A further object is to providesuch apparatus that. eliminates the necessity for spray deflectors andbaffles of prior art devices to prevent mist and flying particles fromcontaminating the coated area of the web. A still further object is toprovide such apparatus whereby excess coating material is recycled,reducing the volume and expense of coating material required from thesource of supply.

A particular object isto provide improved apparatus ,having a novelarrangement of component elements by which viscous water-permeablecolloid silver halide dispersons can be coated continuously as a thinlayer onto a continuous web at a coating speed 'as high as 400 feet perminute to produce a photographic film element of commercial quality anduniformity having satisfactory sensitometric and other photographicproperties. Still other objects will be apparent from the following description of a preferred embodiment of the invention, which will now bedetailed with reference to the accompanying drawing, wherein:

FIG. 1 is a side elevation view of the component parts of the apparatusin operational relationship, with a portion of the coating pan brokenaway for clarity; and

FIG. 2 is a schematic side elevation view illustrating the production ofa coated photographic film utilizing the webcoating apparatus of FIG. 1.

FIG. 3 is a schematic side elevation view illustrating the relationshipbetween certain parts of the web coating apparatus of FIG. 1.

Referring now to the drawing, the principal elements of the apparatus ofthis invention include an air knife 1, a metering device 2, a coatingroll 3 and a coating pan 4, arranged to apply a thin layer of viscousliquid coating material 5 by the skim coating method to the flexible web6 continuously advancing in the direction indicated by the arrows.

United States Patent 0 2,995,469 Patented Aug. 8, 1961 The air knife 1is positioned on and secured to a suitable frame (not shown). The airknife is adjustable as in the prior art to impinge a planar stream ofair at any. desired angle onto the coated web. A trunnion 7 is fastenedat each end of end plate 8 of the air knife near the air oriffice 9.Trunnions- 7 extend ashort distance from the end plate 8 to holdupperbracketslfl of the adjusting mechanism for the metering device 2.The trunnions7 are threaded to receive nuts 11 for securing the upperbrackets 10.

The metering device 2 is positioned so that its metering lip 12 isparallel to the surface of the coating roll 3 and extends laterallyacross the roll for a distance at least as great as the width of the web6 being coated. The metering device is of rigid construction and may besolid or hollow. Besides the metering lip 12, which is preferably amachined projecting portion adjacent the coating roll as illustrated,the metering device has uppersurface 13 and lower surface 14 for guidingexcess coating ma: terial back into the coating pan. Upper surface 13 isshown sloping downwardly in an arcuateprojection 15 to further directexcess material off surface 13 into the coating pan. Trunnion 16for-securing the metering device 2 to its adjusting mechanism is securedat each lateral end of the metering device by means of threads and nutsor, as illustrated, by pinch fits.

The adjusting mechanism is mounted on'the air knife so that the: preciselocation of the metering device can be adjusted independently of the airknife. .As illustrated in FIG. 3, it is important to be able to adjustaccurately the distance Y of the metering lip 12 from the on-running web6, the distance Z between the metering device and'the air orifice 9, andthe angle 0 that the plane of theweb forms with the upper surface 13 ofthe metering device.

The adjusting mechanism in the illustrated embodiment has upper brackets10 and lower brackets.- ..17 suitably interconnected. Adjusting screwor-screws 19 mount.- ed on the upper brackets enable preciseadvancingand retracting of the metering device to adjust'the distance Y of thelip 12 from the web. Adjusting screw or screws 19 similarly enableprecise advancing and retracting of the metering device in aperpendicular direction to adjust the distance Z between the meteringdevice and the air ori-- fice. Rotative adjustment of the meteringdevice about its pivotal mount on trunnions 16 serves to regulate thedesired angle 6 between the web and the upper surface 13 of the meteringdevice. The angle is held by any suitable means such as adjusting screw20.

The coating pan 4 can be of conventional design but is preferablydivided into separate sections as shown. -,A reservoir of coatingmaterial 5 is supplied from any'suit-. able source such as through aninlet pressure feeding from a source outside the pan. The overflow ofcoating material over wier 21 flows into trough 22 which serves as acollecting container for the overflow over wier 21 as well as excesscoating material flowing down surfaces 13 and 14 of the metering device.The wier 21 is'par-allel to the surface of the coating roll 3 and issomewhat lower than the back edge 23 of the pan so overflow from thereservoir will occur only in the direction of travel ofthe web. Coatingmaterial collected in trough 22 is led by any suitable means (not shown)back into the flowof coating material feeding to the reservoir, thuseliminating waste and loss of material. The coating pan can beadjustable in a vertical direction and in a right and left direction topermit positioning of the coating pan at the precisely desired locationduring operation.

Maintenance of the variables referred to above critical defined limitsof position to produce the surprising results herein described will nowbe set forth.

The coating pan must be in a position relative to web to apply a surfacecoating of the coating material within the.

I leaves the coating pan.

onto the web in a thickness of at least 200% of the final wet coatingthickness X desired. It'is preferred that a thickness of coatingmaterial of from 450% to 550% of the final wet coating thickness be lefton the web as it It is preferred that the thickness of the coatingapplied at the coating pan be controlled by using the wier or forwardedge of the coating pan as a metering or doctoring blade.

The metering device 2 is preferably positioned with its metering lip 12adjacent the web at the place where the web changes direction of forwardtravel from an arcuate path around the coating roll to a straight planarpath leading to subsequent web handling equipment. In other words, it ispreferred that the metering lip 12 be located immediately preceding thepoint at which the outrunning web leaves contact with the coating roll.In this preferred position, the jet from the orifice 9 impinges on thecoating material on a portion of the web which is still in contact withcoating roll 3.

It is essential that the metering lip 12 be positioned close enough tothe web that the lip acts to remove a part of the freshly applied excesscoating material. The outstanding results obtainable according to thisinvention require that there be no gap or space between the lip and thecoating material on the web. It is important that no air, particularlyfrom the air knife, be permitted to pass between the lip and the web. Ithas been found necessary to position the lip 12 so that it permits anexcess of coating material to pass the lip 12. In particular, the amountof coating allowed to pass the lip as illustrated in FIG. 3 (or, inother words, the distance Y from the lip 12 to the web 6) must be 'atleast 120%, and preferably 120% to 150%, of the final wet coatingthickness X.

The material that is metered by the lip 12 flows down the lower surface14 of the metering device 2 in a smooth stream to the trough 22. Theangle of position of the lower surface 14 will depend on the shape andconstruction of the metering device and is not critical.

The air knife must be positioned to direct a stream of air against thecoated web at an angle, measured from the plane of the outrunning web(or from the plane of tangents to the roll through the line ofimpingement of the air stream, if applicable), of from 35 to 90, andpreferably from 45 to 55. This angle is measured counterclockwise fromthe plane of the outrunning web.

The distance Z from the line of impingement of the air stream to the lip12 may vary depending on such variables as the viscosity of the coatingmaterial and the coating speed, and can readily be determined by personsin the art in accordance with the teachings set forth herein. Thedistance Z for most coating operations generally will be from 1.0 to 5.0times. and preferably from 2.0 to 3.0

times, the final wet coating thickness.

The angle formed by the upper surface 13 of the metering device 2 andthe plane of the web at the line of metering by lip 12 has been found tobe critical. This angle is measured counter-clockwise from the uppersurface 13 and is herein referred to as the angle between the uppersurface of the metering device and the plane of the web. It is importantthat this angle between the upper surface of the metering device and theplane of the web be at least as large, and preferably to 15 larger, thanthe angle at which air impinged on the coating material is reflectedawayfrom the coated surface of the web. Operating in this relative positioninsures the stability of the flow of air and excess coating material,which is passing downwardly over surface 13. It should be pointed outthat the angle of impingement of air from the air knife will notnecessarily be equal to the angle of reflection of the air stream.

In operation, the flexible web is passed around the coating roll,coating material to be applied is delivered aqueous photographicmaterials.

in the coating of aqueous silver halide dispersions in the to thecoating pan, and the various elements of the apparatus are positioned asdescribed above to effect the coating of a thin layer on the web. Withthe wier acting partially as a doctor blade, coating material metered byit remains in the coating pan. Coating material metered by the lip 12flows smoothly and steadily downwardly on surface 14 into the trough.Excess coating metered by the air stream from the air knife, which inprior art air knife coating installations may run back down the web orfly from the webas' a spray, mist or fog-of particles, is returned tothe coatingpanin a smooth stream flowing downwardly along the uppersurface 13 of the metering device. The possibilities of streaks beingformed by the coating material running down the web and the spray, mistor fog settling on and injuring the smoothed portion of the coating areeliminated by this invention.

This invention is particularly useful in the coating of It is especiallyuseful various types of natural and synthetic water-permeable colloidsas binding agents for the light-sensitive silver halide grains,including gelatin, albumin, agar-agar, water-permeablepolyamides,polyvinyl alcohol, partially hydrolyzed polyvinyl esters, hydrophilicpolyvinyl acetals including those containing color-former nuclei, andother types of viscous aqueous solutions, particularly those containingcolloids.

A preferred use for this invention is in the coating of gelatino silverhalide emulsions. FIG. 2 of the drawing schematically represents aconvenient arrangement of operations conventionally used for suchcoating.

Referring to FIG. 2, a supply of web, e.g., film base or paper, fromunwind source 24 travels around guide roller 25 in the directionindicated, around the coating roll 3.at the coating station (see FIG.1), past guide roller 26, through a conventional chill area 27 where theemulsion is set, around guide roller 28, through a conventional dryer29, and then to windup 30 or other processing operation. Otherairangements may of course be used, as will be readily understood bypersons in the art.

While not wishing to be limited by the following explanation, it isbelieved that the reason for the outstanding results obtainable underthe conditions outlined above is that the air stream from the air knife,after it has cu off the last excess coating material, is stabilized bythe metering device 2 after the air is reflected from the coating andtravels in a-smooth non-turbulent stream along the upper surface 13 ofthe metering device. This appears to effect the holding of the excesscoating material on the upper surface 13 and directs the flow of thematerial evenly and smoothly into the trough of the coating pan.

An additional reason for the excellent results, particularly at highcoating speeds, is believed due to the fact that, as the excess coatingmaterial is cut from the web by the air stream from the air knife, asmall puddle or head of material is formed at the upper part of thejuncture between the outrunning web and the upper edge of the meteringdevice. This puddle in effect serves as a reservoir supplying materialto any voids which exist in I the coating. In this manner, a uniformsurface of coat- 'minute i 'Ili'erinvention;will;beefurther explained.but is not intended .to tber-limited -by;:the=;:fllowifig examples:

Example; I

Apparatus as illustrated ,lll'l'i' F-IG. 1 of the drawing is arrangedwith' the air streann dir'ected .to impinge on the coated "Web at: anangles ofwabouttSZ. from the plane oft'ithe outrunning webi 'Ili'eair:knifeispositioned'0.1 inch from the :web. The :air;tkniferpressuretis '5 :78 inches of L'Water "using an orificeeof 0;.025inchi The metering device is adjusted withitherrnetering lip; 12Jat adistance oft t 0.013 inch; from the :webi That-distance. between theline at whichitthexair streamztfrom the-:airiknife' :impinges onrthecoatinggand the upper edge of the lipof the meter-. irigidwic'edsiOiOBOinchl" Theangle'formed between the planeof ith'e:aveb*i(asfdefinedabove) and: the upper surfa'cecofl thermetering ,device :is about i 68 Acellulose acetate z fil'ihr. base :12 moving; at a speed of 220 feet peroatedrwithbm galati'rio silver bromochloridc light-sensititiephotographic emulsion v "havin g a a viscosity of- .10.6 F centistokeswat Latemperaturerof "100 F;' and a solids-:content iof 516%,] byaweig'htr, A coating got about l39img." of solids per tsquareadecimeter-is obtained. The result'antzremulsion coatedtflm vhas excellentnqualityand uniformitiywof .sensitbthetricizand.iother :propertiess.

Example. II t Eiramplewl Eis zrepeatedlexcept that' theair knife pres-.-

inches: ofifwater; the: distance between the:

sure is 3n :andth :web: device A ang e. .:with"respect:ttoothe web is.about. 65

graphic emulsion of the Xray;.type:havingaaviscosity of 26=Tcentistokesatla temperatureeofil 00 9 andta "16% by weight solids content-rtistcoatedliontoa gelatin :subbed polyethylene rterephthalatawebkrnoving,at. about :1 50 feet I pertrninutex; A'tcoating'zof i'about;:227 7mg:of solids per square "decimeter havingsexcellent; quality and propertiesisobtainedzasxiriz'liiiample Ex'amplellll 1 Estampletl ."is repeated'except 'that ltheudistance betwcen the metering elip andthe=.webis-.-0OO7 inch. A'web ofpapersoft. the-slight: weight: document.stock type moving att ab'outi ISO-"feet per minute is. coated with 1a.gelatino ample 1L Tlie a.coating ".operationris notuliinited to skimcoating; methods but iszalsotusefuli wherein thetapplicationof'thecoatingumaterial t to: the awebi is' :accomplished f by other methodsvutilizing zan a extrusion coating;v etc.

In additio'ntto" silver halide :emulsions,- the invention isuseftibfim-the;applicationeofisuch coating materials as gelatinsublayeis; gelatint'fil'tervlayers; antiabrasion layers,

antistatic-z layers, etcr Th'einventionis also useful in" applyingpigmented layers tofilihs andpaper webs. Other useswillireadily occurtopersons in the art.

lt'fiwill beunderstoodthat meet the apparatus of thisinvention,andequivalentapparatus inthe herein describedmanneryis,directed toasnovel process for coating a con-- tinuousflexible .wcb'to 'apply' a'coatcd layer of coating material having a.pre'selectedztlesired final thickness (cone veniently-referredetotas-measuredtwhile wet; although dry thicknessrcalculationscouldz'ireadily' be used :with" corre-' spondihgtchanges'=inxtherranges=zset forth below)$ The process comprises =applyirigvto'i-themoving web coating; materialt im atrelativ'ely -thick layer having a"thickness of knife. 0- elfect' smoothing of the: coating;v Intadditionntorskim coating, such methods. iri cludecdip, coating .niprolLfcoating; reverse roll coating,"

'.020 inch, and theunetering An' aqueous 'gelatino-sil'veriodoeo'romidedightrsensitive photo-- at lenti 00%; and preferablyt450%-to.550%";of.;the*

desiredofinal ;wet thickness metering at a first line-:tr'ans;

verse acrossthe .web the relatively thick layer to a3lesser thicknessof-at least Y%, and preferably 120% to of -tli'e :desir'ed 'final wetthickness; impinging at asecond linewtr'ansversetacross the web a streamof *air against the clayer'of:lesser' thickness at'an'angleof 35.?" to90, and preferably-45. to .50", measured fromathe plane of the'web atthe secondtransverseline IQS dOCtOE-T the layer of lesser.thicknessttoithe desired final thickness,-e. the secondtrnnsverseliriecbeingat a distanceifrom the first": transverse lineofaboutr-LO to 5.0 times, and preferablyfrom 2.0 to3.-O-times,"therdesired final wet thickness, and

guiding the-air stream reflected from the second transverse line awayfrom the web'tzat. an angle measured froniath'e': plane of the web atthefirst transverse '-line..o.at.:least as large, and preferably 5? to 15larger, than thezanglesof ithe reflected "air stream alsotmeasureddfromxtheeplane of thetweb atr the -first transverse-line;whil'enpreventin'g-aa the-passage of any air fromtheimpingin'gwr'reflectedii stream from eftectingtcontact directlywithftthe inrunningg;

prevention of the Hcoating-Jrnaterial .beinggimetereda from. the web:.bythe metering device. from. returning along athea surface :of the web;thus obviating a.defectof zprior tartfi coatingapparatus'and methods,namely, theidefect :which-i, appearsas bands ofcoatingmaterialofatthickness heavier: than desired. running .in the. direction of the.weblztravelzi By carrying; out the .present inventionp these'longitudiiialai bands t orstripes are eliminated' Anotherradvantage-cuis that by, controlling .;the -:path=. of=:thercoatinggmaterialsdoci-- toredzby the. air 'knife,: .not material: isthrown: fromnthel web atshigh speeds as spray,- mist lor;fog,-t .thus"-reducinggi, the-danger 'of coating. material. contaminating'i andfiors' otherwise injut'ing-thczsmoothed' coating surface; Yet any otheradvantage resides in the fact that. coatings-can; made-over a :widerange of speeds by' apparatus th'at easily adjustable and accessiblefor'cleaning.andnmaiti e. nancer Afurther advantage is that=exeesscoating-material); is not 'wastc dtbut can be conveniently recycled;thus (re ducing the amount neededandtheexpense .of;complicated salvagingequipment. A stillfurther:advantage-isthatth air stream from-z-theairknife isscompletelydeflected? 0- that it. cannot disturb the surfaceofthetcoatingrmateria'l in .the:.coatingpan at thcspointat.which'.the'-weba' c011= tacts thecoating:material..inithetpan;

An additional advantage is thnttheair streamis'ista'bi-ilizccl,eliminating air. jet. chatter :by the proximitytof the upper surface otthe metering -.device .to the lineiof fima pingement of the airstream,vand.by maintaining-thethick I; ness of the layer .to beair'doctored relatively constant. b'yl: the :action of the meteringdevice.:-Yetaafurtherradvanl-r tage is .th at the .entire smoothing apparatuscan; be iconveniently moved out of operating position and returned? tooperatingtposition with the-air knife in 'a SiHgIG'HIOtiOIiE- A particular advantage resides inthefact. that light sen si tive photographicemulsions can"besapplie'd top l 1oto-'- graphic .film base at spcedsiashigh as 400feet per minute-i to obtain coated photographicfilihsof'outstanding smoothE-i ness and uniformity; of 'quality;.withlsatisfactory-tsenst-i tometric and other photographicproperties. still'lotherl" advantages will be apparent fr'omthe above-z descriptions: ofthe invention.

An advantage of the present; invention; residesinsthe The inventionclaimed is:

1. A process of web coating comprising applying to a flexible moving webcoating material in a relatively thick layer having a thickness of atleast 200% of the desired final wet thickness, metering at a firsttransverse line across the web said relatively thick layer to a lesserthickness of at least 120% of said desired wet thickness, impinging at asecond transverse line across said web a stream of air against saidlayer of lesser thickness at an angle of 35 to 90 measured from theplane of said web through said second transverse line to dostor saidlayer of lesser thickness to said desired wet thickness, said secondtransverse line being at a distance from said first transverse line ofabout 1.0 to 5.0 times said desired wet thickness, and guiding said airstream reflected from said second transverse line away from said web atan angle, measured from the plane of said web at said first transverseline, at least as large as the angle of said reflected air streammeasured from the plane of said web at said second transverse line,while preventing the passage of air from said impinging-stream and saidreflected stream from effecting contact with the inrun'ning web at anyportion of said web preceding said first transverse line.

2. A process as set forth in claim I wherein said coating material is aviscous aqueous solution of a waterpermeable colloid.

3.. A process as set forth in claim 2 wherein said coating material isan aqueous gelatino silver halide dispersion.

s 4. A process as set forth in claim 1 wherein said relatively thicklayer has a thickness of 450% to 550% of said desired wet thickness.

5. A process as set forth in claim 1 wherein said layer of lesserthickness has a thickness of 120% to 150% of said desired wet thickness6. A process as set forth in claim 1 wherein said angle of said streamof air is 45 to 55.

7. A process as set forth in claim 6 wherein said distance is 2.0 to 3.0times said desired wet thickness.

8. A process as set forth in claim 6 wherein said guiding is at an angleof to 15 greater than the angle of said reflected air stream.

9. In an apparatus for coating a moving flexible web to a desired wetthickness (X) comprising a coating roll layer of coating material,arotatably mounted air knife doctor having an air orifice adjacent tothe traveling web for directing a stream of air against the coated layerat an impingement line transverse to the direction of web travel, saidangle of impingement ranging from 35 to from the plane of the outrunningweb at the impingement line, the combination with said air knife doctorof a metering device, said metering device being connected .to said airknife doctor and beinglocated between said coating means and said airknife doctor, the metering device comprising an upper fluid deflectingsurface and a lower liquid smoothing surface having a lip portionadjacent and parallel to the surface of the web, said lip portionforming an apex with the upper fluid deflecting surface, said meteringdevice being precisely adjustable horizontally, vertically androtatively in relation to the web independently of the air knife doctorby an adjusting mechanism having separate screw adjustments, said,adjusting mechanism being mounted on the air knife doctor whereby thedistance (Y) of the metering lip from the web, the distance (Z) from theapex of the metering device and the air orifice of the air knife doctorrange from 1.2X to 1.5X and X to 5X, respectively, and the angle 0measured from the said upper fluid deflecting surface counterclockwiseto the plane of the web as the web passes the metering lip is at'leastas great as the angle of the air being deflected from the coated surfaceof the web.

References Cited in the file of this patent UNITED STATES PATENTS GreatBritain Ian. 9, 1930

1. A PROCESS OF WEB COATING COMPRISING APPLYING TO A FLEXIBLE MOVING WEBCOATING MATERIAL IN A RELATIVELY THICK LAYER HAVING A THICKNESS OF ATLEAST 200% OF THE DESIRED FINAL WET THICKNESS, METERING AT A FIRSTTRANSVERSE LINE ACROSS THE WEB SAID RELATIVELY THICK LAYER TO A LESSERTHICKNESS OF AT LEAST 120% OF SAID DESIRED WET THICKNESS, IMPINGING AT ASECOND TRANSVERSE LINE ACROSS SAID WEB A STREAM OF AIR AGAINST SAIDLAYER OF LESSER THICKNESS AT AN ANGLE OF 35* TO 90* MEASURED FROM THEPLANE OF SAID WEB THROUGH SAID SECOND TRANSVERSE LINE TO DOCTOR SAIDLAYER OF LESSER THICKNESS TO SAID DESIRED WET THICKNESS, SAID SECONDTRANSVERSE LINE BEING AT A DISTANCE FROM SAID FIRST TRANSVERSE LINE OFABOUT 1.0 TO 5.0 TIMES SAID DESIRED WET THICKNESS, AND GUIDING SAID AIRSTREAM REFLECTED FROM SAID SECOND TRANSVERSE LINE AWAY FROM SAID WEB ATAN ANGLE, MEASURED FROM THE PLANE OF SAID WEB AT SAID FIRST TRANSVERSELINE, AT LEAST AS LARGE AS THE ANGLE OF SAID REFLECTED AIR STREAMMEASURED FROM THE PLANE OF SAID WEB AT SAID SECOND TRANSVERSE LINE,WHILE PREVENTING THE PASSAGE OF AIR FROM SAID IMPINGING STREAM AND SAIDREFLECTED STREAM FROM EFFECTING CONTACT WITH THE INRUNNING WEB AT ANYPORTION OF SAID WEB PRECEDING SAID FIRST TRANSVERSE LINE.